Large format ion implantation applications, such as implantation into silicon substrates or into large area flat panels, may employ extra wide ion beams having width between 0.5 to 6 meters. Ion implantation is often performed using an ion beam of positively charged ions which may be neutralized near a substrate surface using electrons in order to prevent charge buildup on the substrate.
In conventional technology a plasma flood gun may be used to generate electrons for neutralization of the ion beam proximate a substrate surface. The plasma source in conventional plasma flood guns may contain a plasma chamber wherein a plasma is generated through ionization of atoms of an inert gas such as argon (Ar), xenon (Xe) or krypton (Kr). The plasma flood gun is positioned proximate the ion beam so that electrons from the plasma may diffuse into the ion beam and drawn towards the target substrate to neutralize positive charge on the substrate.
One issue that arises with the use of present day plasma flood guns is that of metal contamination. In particular, certain conventional plasma flood guns use a hot tungsten filament for plasma generation in an arc discharge. When the hot tungsten filament reaches a sufficient temperature, electrons may be emitted and accelerated to ionize gaseous species to create the plasma. This type of plasma flood gun may generate sufficient plasma density (≧1013 cm−3) to produce a flux of electrons to neutralize an ion beam proximate a substrate surface. However, during operation, the tungsten filament is gradually consumed by sputtering and evaporation and tungsten atoms may contaminate the ion implantation system. Moreover, these tungsten atoms may be ionized in the plasma and transported through the beam line toward the substrate thus compromising the semiconductor structure functionality.